An information displaying medium is a promising information transfer means formed by providing a card, i.e., a base sheet, with a repeatedly writable displaying unit and capable of displaying different pieces of information as occasion demands. The information displaying medium when used, for example, as a customer card, services to the customer can be improved by displaying messages and such on the information displaying medium.
Various writable, reversible displaying elements intended for use for forming writable displaying unit have been proposed. Heat, light or magnetism is used for recording information on and erasing recorded information from the reversible displaying element. A reversible displaying element employs a fatty acid dispersed polymer film formed by dispersing a fatty acid that changes its phase between an opaque phase and a transparent phase in a polymer matrix. Another reversible displaying element uses the reversible opening and closing of lactone rings of a leuco dye by a developer/subtracter agent. A third reversible displaying element employs a polymer liquid crystal. A fourth reversible displaying element employs microcapsules containing magnetic powder.
The visibility of those known reversible displaying elements will be examined. The reversible displaying element employing a leuco dye indicates blue images on a white background and becomes light blue in an erased state. The reflection densities of the background, the images and the erased state measured by a Macbeth reflection densitometer (RD-918) are about 0.1, about 1.5 and about 0.3, respectively. Although the initial visibility is satisfactory, residual images remain after erasing. The reversible displaying element employing a fatty acid dispersed polymer film indicates white images of 0.4 in reflection density on the background of 1.2 in reflection density having metallic luster and has metallic luster in an erased state of 1.2 in reflection density. White characters displayed on the background having metallic luster is difficult to recognize and the visibility of the reversible displaying element is unsatisfactory.
The reversible displaying element employing microcapsules containing magnetic powder displays black images of 1.5 in reflection density on a silvery background of 1.0 in reflection density and becomes silvery in an erased state of 1.0 in reflection density. The visibility of black characters on the silvery background is unsatisfactory.
The reversible displaying element employing a polymer/liquid crystal composite film, when used in combination with a black dichroic dye, displays black images of 1.4 in reflection density on a white background of 0.5 in reflection density and becomes white in an erased state of 0.5 in reflection density. Black characters displayed on the white background are easy to recognize, the visibility of the reversible displaying element is excellent and residual images may not remain after erasing.